This invention relates to an optical scanning device used for an image forming apparatus utilizing an electrophotographic technique such as a laser printer or the like, and more particularly to an optical scanning device using an optical waveguide array.
In Japanese Patent Application No. 1-309220 (not prior art), the same applicant as this application has proposed an optical scanning device for scanning a light beam on a photosensitive drum of an image forming apparatus using an optical waveguide array to form an electrostatic latent image on the photosensitive drum. In this optical scanning device, plural optical waveguides are arcuately arranged at one end of the device and straightly or parallel arranged at the other end. The arcuately arranged end serves as a light incident end for receiving a modulated light beam from a light source, and the straightly arranged end serves as a light emitting end for emitting the modulated light beam passing through the optical waveguides. Each of the optical waveguides comprises two kinds of materials having different refractive indexes to the light beam from the light source. In more detail, as shown in FIG. 1, a core portion 41 having a higher refractive index is formed at the center portion of the optical waveguide, and a cladding portion 42 having a lower refractive index is formed so as to surround the core portion 41. An interval (core pitch) W between the centers of cores of neighboring optical waveguides is set to a distance which is determined by a resolution of the image forming apparatus using the optical scanning device. For example, when the resolution of an output image is 300 DPI (dot number per inch), the core pitch W is set to approximately 85 microns because a dot (pixel) interval of the image is approximately 85 microns.
As described above, in the optical scanning device having the above arrangement of the optical waveguides, the core interval W between the core portions 41 is equal to the dot (pixel) interval. Accordingly, when each of the light beams which are distributed by a light beam distributing means is converged into a spot beam having a diameter below less than a dot (pixel) interval determined by a resolution, and is incident to a light incident end of each optical waveguide of the optical scanning device, those light beams whose lights are incident on the cladding portion 42 do not reach the photosensitive drum, so that an image quality is deteriorated due to lack of those light beams.